Reland of Make default media device ID salts random by default

content/browser/resource_context_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/resource_context_impl.h"
 
 #include <stdint.h>
 
+#include "base/base64.h"
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/rand_util.h"
 #include "content/browser/blob_storage/chrome_blob_storage_context.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/loader/resource_request_info_impl.h"
 #include "content/browser/streams/stream_context.h"
 #include "content/browser/webui/url_data_manager_backend.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
 #include "net/base/keygen_handler.h"
 #include "net/ssl/client_cert_store.h"
 
 using base::UserDataAdapter;
 
 namespace content {
 
-namespace {
-
 // Key names on ResourceContext.
 const char kBlobStorageContextKeyName[] = "content_blob_storage_context";
 const char kStreamContextKeyName[] = "content_stream_context";
 const char kURLDataManagerBackendKeyName[] = "url_data_manager_backend";
 
-// Used by the default implementation of GetMediaDeviceIDSalt, below.
-std::string ReturnEmptySalt() {
-  return std::string();
-}
-
-}  // namespace
-
-
-ResourceContext::ResourceContext() {
+ResourceContext::ResourceContext()
+    : media_device_id_salt_(CreateRandomMediaDeviceIDSalt()) {
   ResourceDispatcherHostImpl* rdhi = ResourceDispatcherHostImpl::Get();
   if (rdhi) {
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,
         base::Bind(&ResourceDispatcherHostImpl::AddResourceContext,
                    base::Unretained(rdhi), this));
   }
 }
 
 ResourceContext::~ResourceContext() {
   ResourceDispatcherHostImpl* rdhi = ResourceDispatcherHostImpl::Get();
   if (rdhi) {
     rdhi->CancelRequestsForContext(this);
     rdhi->RemoveResourceContext(this);
   }
 
   // In some tests this object is destructed on UI thread.
   DetachUserDataThread();
 }
 
-ResourceContext::SaltCallback ResourceContext::GetMediaDeviceIDSalt() {
-  return base::Bind(&ReturnEmptySalt);
+std::string ResourceContext::GetMediaDeviceIDSalt() {
+  return media_device_id_salt_;
 }
 
 std::unique_ptr<net::ClientCertStore> ResourceContext::CreateClientCertStore() {
   return std::unique_ptr<net::ClientCertStore>();
 }
 
 void ResourceContext::CreateKeygenHandler(
     uint32_t key_size_in_bits,
     const std::string& challenge_string,
     const GURL& url,
     const base::Callback<void(std::unique_ptr<net::KeygenHandler>)>& callback) {
   callback.Run(base::WrapUnique(
       new net::KeygenHandler(key_size_in_bits, challenge_string, url)));
 }
 
+// static
+std::string ResourceContext::CreateRandomMediaDeviceIDSalt() {
+  std::string salt;
+  base::Base64Encode(base::RandBytesAsString(16), &salt);
+  DCHECK(!salt.empty());
+  return salt;
+}
+
 ChromeBlobStorageContext* GetChromeBlobStorageContextForResourceContext(
     const ResourceContext* resource_context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   return UserDataAdapter<ChromeBlobStorageContext>::Get(
       resource_context, kBlobStorageContextKeyName);
 }
 
 StreamContext* GetStreamContextForResourceContext(
     const ResourceContext* resource_context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
@@ skipping 22 matching lines @@
 
   resource_context->SetUserData(
       kStreamContextKeyName,
       new UserDataAdapter<StreamContext>(
           StreamContext::GetFor(browser_context)));
 
   resource_context->DetachUserDataThread();
 }
 
 }  // namespace content